Polymerization catalyst system and process



United States Patent Cfitice 3,32%,224 Patented May 16, 1967 3,320,224POLYMERIZATION CATALYST SYSTEM AND PRUQESS William J. Raich, Midland,and Maurice R. Peacock,

Wheeler. Mich, assignors to The Dow Chemical Company, Midland, Mich, acorporation of Delaware N Drawing. Filed Jan. 27, 1964, Ser. No. 340,5368 Claims. (Cl. 260-9.).7)

This invention relates to a new and improved polymerization process andis particularly concerned with the use of a novel heterogeneous catalystcomposition for preparing high molecular weight solid polyolefins, suchas polypropylene, having a high isotactic content.

In the polymerization of propylene and other olefins, it has been foundthat with heterogeneous catalyst systems, such as complexes formed fromTiCL, with aluminum alkyls, such as AlEt etc., TiCl plus AlEt etc.,there is a substantial portion of amorphous or atactic polymer formed.These atactic polymers have a random polymer structure whereas thedesired isotactic type of polymer has a stereospecific type of structurein which the side branches from the linear chain are arranged in aregular repeating type of arrangement which gives desired crystallizablestructure and resultant desired qualities in the polymer.

The isotactic polymer of propylene, is a hard, tough, high melting(165-175 C.) and highly crystalline material (6575% by X-raydetermination) which is insoluble in hot hexane.

In contrast, the atactic polymer may range from a grease-like toWax-like material depending upon its molecular weight, but regardless ofmolecular weight is soluble in hot hexane.

The amount of isotactic polymer contained in the total polymer productformed in any given polymerization appears to have a significantinfluence on certain properties of the polymer product, such ashardness, modulus, ultimate tensile strength, range of meltingtemperatures, and molding and fiber forming properties. The higher theisotactic content of the polymer, the more outstanding are the physicalroperties of that polymer.

A number of catalyst systems have been tried in an attempt to avoid orto reduce to a permissible amount the formation of such atactic polymersas byproducts in the production of the desired isotactic polymericolefin. While certain catalyst systems give some small decrease in theamount of atactic byproduct, they produce side effects which are almostas disadvantageous, such as a decrease in the yield of polymer. Certainother catalyst systems actually increase the amount of atactic material.In other words, most polymerization catalyst systems either arenoneffective in reducing the amount of such byproduct formed or wherethere is any improvement in this respect, certain other disadvantagesresult to offset such improvement.

It is an object of this invention, therefore, to provide an improvedprocess for producing isotactic polymers.

Another object of the invention is to provide a process for preparingpolymers having isotactic contents which are higher than those ofconventionally prepared polymers.

A further object of the invention is to provide a process in whichincreased yields of isotactic polymers are obtained.

Other and further objects and advantages of the invention will becomeapparent to those skilled in the art upon consideration of theaccompanying disclosure.

According to the present invention, olefin polymers of very highisotactic content can be prepared by conducting the polymerization inthe presence of a catalyst mixture comprised of a trialkylaluminum, ahalide of titanium,

and a dialkylaluminum cyclopentadiene. By the use of this catalystcomposition, the proportion of atactic polymer formed in thepolymerization of propylene, butene-l, and other olefins which normallyform substantial amounts of atactic polymer byproduct in heterogeneouscatalyst systems, can be reduced without any disadvantageous sideeffects to an amount which is not harmful to the properties of thedesired polymer. In addition, the catalyst composition is beneficial inincreasing the yield of isotactic polymer over that otherwiseexperienced.

Any a-olefin can be polymerized according to the present invention. Bythe term a-olefin is meant any compound which can be represented by theformula where R is hydrogen or an alkyl, cycloalkyl, or aryl group.Examples are ethylene, propylene, l-n-butene, 3-methyl-1-butene,l-n-pentene, 4-methyl-l-pentene, l-nhexene, and aromatic vinylhydrocarbons such as for example styrene and its homologues. Theseolefins can be polymerized alone to form homopolymers, or as mixtureswith each other to form valuable copolymers. Particularly useful resultsare obtained from the polymerization of aliphatic a-clefins such as forexample, propylene.

The trialkylaluminum component of the catalyst mixture of the presentinvention can be represented by the general formula R" Al, wherein R" isan alkyl radical, preferably containing from 1 to 12, inclusive, carbonatoms. Examples of compounds corresponding to the aforementioned formulawhich can be used include trimethylaluminum, triethylaluminum,triisobutylaluminum, tri n butylaluminum, tri-n-pentylaluminum,triisooctylaluminum, tri-n-dodecylaluminum, and the like.

The titanium halide component of the catalyst mixture of the presentinvention may be any of the titanium halides including the chloride,bromides, and iodides, the trichlorides of titanium being preferred.

A particularly suitable heterogeneous catalyst system of this inventionis one using TiCl preferably in the alpha form, and an aluminumtrialkyl, such as aluminum triethyl. In such a catalyst system, it isfound desirable to have an Al-Ti ratio of approximately 0.5-10 moles ofaluminum compound per mole of Ti compound. A particularly suitable ratiois 2 moles of aluminum compound per mole of titanium compound. Otherexamples of such catalyst systems include triisobutylaluminum andtitanium trichloride, tri-n-dodecylaluminum and titanium trichloride,titanium tribromide and tri-n-butylaluminum, titanium tribromide andtriisooctylaluminum, titanium tetrachloride and triisobutylaluminum,titanium tetrabromide and tri-n-heptylaluminum, and titanium tetraiodideand triethylaluminum.

Typical examples of the dialkyl aluminum cyclopentadiene compoundsinclude dimethyl, diethyl, dipropyl, dibutyl, diisobutyl, and dihexyl,aluminum cyclopentadiene.

The dialkyl aluminum cyclopentadienes are prepared by exchange reactionsbetween dialkyl aluminum halides and metal cyclopentadienides such assodium, or lithium cyclopentadienide or magnesium dicyclopentadienide.

The ratios of the catalyst components employed in the present processcan be varied rather widely, depending upon the particular monomer usedand the operating conditions. The mole ratio of the trialkylaluminum tothe titanium halide is usually in the range of 0.5:1 to 10:1 with thepreferred range being 1:1 to 4:1. The amount of dialkyl aluminumcyclopentadiene included in the catalyst mixture is generally in therange of 0.01 to 0.5 mole per mole of titanium halide, .02 to 0.1 molebeing preferred.

The concentration of titanium halide catalyst in the polymerization zoneis usually in the range of 0.1 to 0.5 weight percent, based on the inertpolymerization vehicle charged to that zone.

The polymerization reaction is carried out with the components of thereaction dispersed throughout an inert liquid vehicle and, when thea-olefin to be polymerized is normally a gas, the latter can be bubbledthrough the liquid vehicle which contains the catalyst system. Examplesof the preferred liquid vehicles are aliphatic, cycloaliphatic, andhydrogenated aromatic hydrocarbons, such as pentane, hexane,cyclohexane, heptane, tetrahydronaphthalene, decahydronaphthalene, thehigher paraffins, and mixtures thereof. Aromatic hydrocarbons such asbenzene, xylene, halogenated aromatic hydrocarbons, such asorthodichlorobenzene and chlorinated naphthalene and mixtures thereofmay also be used.

Generally, the polymerization of this invention can be conducted in arather broad temperature range, namely, from about room temperature toabout 150 C., preferably in the range of 5575 C. However, improvedelfects of this catalyst system are observed at temperatures even belowroom temperature.

It is unnecessary to employ elevated pressures in order to bring aboutthe polymerization of a-olefins according to the present invention.However, for convenience of handling normally gaseous olefins, such asethylene and propylene, it is sometimes advantageous to employ slightlyelevated pressures. Most suitably the present invention is carried outunder a pressure between atmospheric and 500 pounds per square inchgauge (p.s.i.g.). For the polymerization of polypropylene, a pressurerange of p.s.i.g. to 100 p.s.i.g. is desirable.

The preparation of the catalyst system and the subsequent polymerizationare preferably carried out in the absence of molecular oxygen, carbonmonoxide, carbon dioxide, and 'water. Most suitably, all reactions arecarried out in an atmosphere of the olefin being polymerized if this isa gas, or, if the olefin is a liquid, in an atmosphere of an inert gassuch as nitrogen. The catalyst systems or their components are destroyedby reaction with oxygen, carbon monoxide, carbon dioxide, or water; andconsequently, if any of these are present in excess, no polymerizationwill take place.

Polymerization according to the process of the present invention can bebrought about by mixing the essential components of the catalyst systemin a suitable inert liquid vehicle and then adding the a-olefin to thecatalyst system so formed. The process may be carried out batchwise orcontinuously and by its use high yields of isotactic polymers can beproduced. The residence time used in a continuous process can varywidely since it depends to a great extent upon the temperature at whichthe process is carried out and upon the specific olefin that is to bepolymerized. However, the residence time in a continuous processgenerally falls within the range of one second to an hour or more. In abatch process, the time for the reaction can also vary widely, such asfrom minutes up to 24 hours or more.

Upon completion of the polymerization reaction, any excess olefin isvented and the contents of the reactor are then treated by any suitablemethod to inactivate the catalyst and remove the catalyst residues. Inone method, inactivation of the catalyst is accomplished by washing withan alcohol, water, or other suitable materials. The isotactic polymer isthen separated from the diluent, e.g., by decantation, filtration, orother suitable method after which the polymer is dried.

The atactic polymer may be recovered from the filtrate by suitableevaporation techniques.

The practice of this invention is best illustrated by the followingexamples. The techniques and conditions normally used in heterogenouscatalyst systems are suitable for the practice of this invention. Theseexamples are given merely by way of illustration and are not intended tolimit the scope of the invention in any way nor the manner in which theinvention can be practiced. Throughout the specification, wherereference is made to polymers and polymerization, it is intended thatthese terms embrace copolymers and copolymerization unless otherwiseindicated.

EXAMPLE I As a test, not exemplary of the present invention, propylenewas polymerized in the following manner.

To a stirred autoclave jacketed to control temperature which had beenpreviously evacuated to prevent the catalyst from coming in contact withair was charged one liter of dry hexane, in which was dispersed acatalyst composition comprised of 2 millimoles of a-TiCl and 4millimoles of triethyl aluminum. The autoclave was then pressurized toone atmosphere total pressure with propylene gas and then heated to 75C. The propylene pressure was raised to 50 p.s.i.g. and stirring andheating of the mixture was continued for 1.5 hours after which time theautoclave was cooled and vented to atmospheric pressure. The catalystwas decomposed by the addition of a small quantity of alcohol and thesolid polymer isolated from the mixture by filtration. There wasobtained after drying a 10 g. yield of polymer, 21% of which was solublein the hexane filtrate, i.e., 21% of the polymer produced was of theatactic form.

EXAMPLE II The procedure of Example I was repeated, with the exceptionthat varying concentrations of diethylaluminum cyclopentadiene weredispersed in the hexane along with the other catalyst components. TableI below summarizes the results obtained with various concentrations ofdiethylaluminum cyclopentadiene, said results indicating that thepresence of small amounts of diethylaluminum cyclopentadienesubstantially reduces the formation of atactic polypropylene. It is alsoapparent that the presence of the diethylaluminum cyclopentadienesubstantially increases the yield of polymer in relation to the amountof polymer produced in Example I where the catalyst is prepared onlyfrom triethylaluminum and flt-Tlclg- In place of diethylaluminumcyclopentadiene in the foregoing example, there can be used otherdialkylaluminum cyclopentadienes with substantially the same results.

What is claimed is:

1. A process for the polymerization of propylene, which compriseseffecting the polymerization in an inert hydrocarbon liquid and in thepresence of a catalyst system consisting essentially of (a) atrialkylaluminum, (b) a titanium trichloride, and (c) a dialkylaluminumcyclopentadiene, the molar ratio of said dialkylaluminum cyclopentadienecompound to titanium trichloride being within the range of 0.01:1 to0.5:1.

2. The process of claim 1 wherein the dialkylaluminum cyclopentadienecompound is diethylaluminum cyclopentadiene.

3. The process of claim 1 wherein the polymerization is effected at atemperature in the range of about 20 to about C. and a pressure of fromnormal atmospheric to 500 p.s.i.g.

4. The process of claim 1 wherein the trialkyl aluminum component of thecatalyst system is triethyl aluminum.

5. A process for the polymerization of propylene, which compriseseffecting the polymerization in an inert 5 v hydrocarbon liquid at atemperature range of about 55 to about 75 C., a pressure from about 10p.s.i.g. to about 100 p.s.i.g., and in the presence of a catalyticmixture consisting essentially of (a) a triethyl'aluminum, (b) atitanium trichloride, and (c) a diethylaluminum cyclo- 5 pentadiene, themolar ratio of said dialkylaluminum cyclopentadiene compound to titaniumtrichloride being within the range of 0.0:1 to 0.521.

6. As a composition of matter, a polymerization catalyst consistingessentially of (a) a trialkylaluminum, (b) a titanium trichloride and(c) a dialkylaluminum cyclopentadiene the molar ratio of dialkylaluminumcyclopentadiene to titanium trichloride being within the range of 0.0:1to 05:1.

7. The composition of claim 6 wherein the trialkyl aluminum compound istriethylaluminum.

8. The composition of claim 6, wherein the dialkyl aluminumcyclopentadiene compound is diethylaluminum cyclopentadiene.

No references cited.

JOSEPH L. SCHOFER, Primary Examiner.

L. EDELMAN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,320,224 May 16, 1967 William J. Raich et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 5, line 8, and column 6, line 2, for "0.0:1", eac occurrence,read 0.01:1

Signed and sealed this 2nd day of January 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

1. A PROCESS FOR THE POLYMERIZATION OF PROPYLENE, WHICH COMPRISESEFFECTING THE POLYMERIZATION IN AN INERT HYDROCARBON LIQUID AND IN THEPRESENCE OF A CATALYST SYSTEM CONSISTING ESSENTIALLY OF (A) ATRIALKYLALUMINUM, (B) A TITANIUM TRICHLORIDE, AND (C) A DIALKYLALUMINUMCYCLOPENTADIENE, THE MOLAR RATIO OF SAID DIALKYLALUMINUM CYCLOPENTADIENECOMPOUND TO TITANIUM TRICHLORIDE BEING WITHIN THE RANGE OF 0.01:1 TO0.5:1.